A patent document 1 discloses a known conventional power steering device control device as follows.
The power steering device control device is employed in a power steering device, which the power steering device includes: a steering mechanism configured to transmit rotation of a steering wheel to steered wheels; an electric motor configured to apply a steering assist force to the steering mechanism; and a motor rotational position sensor configured to sense as an actual axis phase a rotational position of a rotor of the electric motor. The power steering device control device is configured to: sense a phase difference between the actual axis phase and a control phase, wherein the control phase is estimated based on a resistance, an inductance, a sensed electric current value, and a voltage command value of winding of the electric motor, and a steering speed; and compensate for the phase difference, and thereby enhance the efficiency of drive of the electric motor.